The invention relates to optical devices. More particularly, the invention relates to an interleaver/deinterleaver having a folded design such that an optical signal passes through a single crystal multiple times.
As telecommunications usage increases as a result of, for example, increased Internet usage, increased types of communications, population growth, telecommunications providers are required to provide greater voice- and data-carrying capacity. In order to reduce cost and the amount of time required to provide the increased capacity wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) have been developed, which provide increased capacity without requiring new fiber optic cables.
WDM and DWDM technologies combine multiple optical signals into a single fiber by transporting different signals on a different optical wavelengths or channels. Interleaving and deinterleaving of optical channels is typically accomplished with thin film optical filters. However, multiple layers of film are required to interleave and deinterleave multiple channels, which increases the cost and complexity of a component. Another disadvantage of multiple layers of thin film for filtering is that the thin films break down over time, especially when operating under high power conditions.
What is needed is an improved optical device for use with WDM and/or DWDM optical signals. Prior attempts to improve optical devices are disclosed in U.S. Pat. No. 4,566,761 issued Jan. 28, 1986 to Carlsen et al, 4,685,773 issued Aug. 11, 1987 to Carlsen et al, and 5,694,233 issued Dec. 2, 1997 to Wu et al, which are incorporated herein by reference.
Single-pass folded interleaver/deinterleavers are described. The device includes a birefringent assembly and multiple reflective elements. The reflective elements reflect an optical signal received via an input port such that the optical signal makes multiple passes through the birefringent assembly before being directed to a first output port and a second output port. The multiple reflections through the birefringent assembly cause a set of signals included in the optical signal received via the input port to be separated into a first subset of optical signals and a second subset of optical signals, which are directed to a first output port and a second output port, respectively.
In one embodiment, set of half wave plates are positioned between one or more of the reflective elements and the birefringent crystal. The half wave plates are oriented with azimuth angles such that the first subset of optical signals have a first polarization and the second subset of optical signals have a second polarization. In one embodiment, the first and second subset of optical signals includes even and odd International Telecommunications Union (ITU) channels.